1. Field of the Invention
This invention relates to a novel method of producing a membrane of graft copolymer by irradiating a polyolefin film with ionizing radiation before or simultaneously with graft copolymerizing an olefinic monomer having a functional group or a mixture of such monomer and a polyene compound onto the polyolefin. The method is characterized by graft copolymerization wherein the polyolefin base film is reciprocated between a pair of reversing rollers through a mobile roller to absorb continuously the expansion of the film that results from the graft copolymerization.
Such method assures uniform graft copolymerization and provides a membrane of graft copolymer free from wrinkles.
2. Description of the Prior Art
A rapid expansion is being seen in the use of high molecular membranes, especially those having functional groups, in the field of chemical engineering, and they have great potential as membranes for osmotic dialysis, electrodialysis, electrolysis, separators for cells, and other ion exchange membranes. Therefore, attempts are being made in various fields to manufacture functional high molecular membranes of better quality, and several methods have been proposed to date.
One known method is similar to the method of this invention in that it produces a membrane by graft copolymerizing an olefinic monomer having a functional group to a polyolefin film base. The method is superior to other known methods in that it is very simple, that it is capable of synthesizing a great many types of membranes by selecting a suitable base film and an olefinic monomer having a suitable functional group depending upon the use and object, and that it is also capable of synthesizing membranes having two or more types of functional groups. But this method often causes uneven polymerization that results in a heterogeneous membrane having many wrinkles on the surface.